The proposed studies will elaborate the ongoing program which aims to analyze, understand and influence the function and intracellular relationships of the cell's second genetic system, the mitochondria, in normal cells and in oncogenic virus-induced malignancy. We have found distinct mitochondrial alterations that affect the mitochondrial DNA replication apparatus, directly correlated with the phenotypic expression of oncogenic virus-induced transformation. We will use various normal and virus-transformed animal cells, including an ideally controlled system of chick embryo fibroblasts (CEF) infected by wild-type and temperature-sensitive mutants of Rous sarcoma viruses (RSV). The following parameters will be studied: (1) The localization and characteristics of modified bases and drug-induced (e. g. with bleomycin) strand breaks within detailed restriction cleavage maps of the mtDNAs; (2) transcriptional mapping of mitochondrial aminoacylated tRNAs; (3) further characterization of mitochondrial and other cellular DNA polymerases with respect to template specificity, response to inhibitors and repair activity; (4) further analysis of the properties of mitochondrial and nuclear DNA methylases in response to virus-transformation.